Binocular Terms

The high-tech nature of binoculars can leave you confused!  If you are reading about binoculars, you may encounter some unfamiliar terminology.  Here are the definitions of some binocular terms that may help you in your search for knowledge:

Magnification (power) refers to the degree to which the object you are viewing has been enlarged.  For instance, if one is looking through a 7x40 binocular, this means that the binocular is able to enlarge the view by seven times what the human eye would normally see.

Diameter refers to the size of one of the front lenses (objective lens) of the binocular, measured in millimeters.  It is the second number in the equation, hence, a 7x40 binocular means that the lens is 40 mm in size.  The diameter of the lens determines the amount of light getting in.  The bigger the lens, the more clearly one will be able to see. 

Field of view is the area that a person can see while looking through binoculars. Field of view is angular (measured in degrees) or linear (measured in feet).  The larger the field of view, the larger the area being viewed.. 

Close focus (also called near focus) refers to the closest distance between you and the object you are viewing, while it remains in focus.

Detection range refers to the distance, usually expressed in yards or meters, that a person can detect an object while using night vision binoculars.

Exit pupil refers to the diameter of the eye holes.  Having a larger exit pupil creates a brighter image, and is optimal for low-light viewing. 

Exit relief is the distance, measured in millimeters, that binoculars can be held away from the eye, in which one can still see the entire field of view.

Brightness refers to the binoculars' ability to gather enough light to produce a clear picture.  Brightness also effects color.

Resolution refers to the amount of light that passes through the eyepiece of the binoculars.  Higher resolution means higher clarity, producing fine details and a sharp image.

Optical Image Stabilizer (IS) shifts a lens parallel to the image plane. This is what keeps the vision (or picture) from blurring as you move.

Prism refers to the glass inside the binoculars that flips the image upright.  There are two main types of prisms:  porro and roof.

Lens coating refers to the coating placed on lenses to reduce glare. Lens coatings come in a variety of forms, including coated, fully coated, multi-coated, and fully multi-coating.  Fully multicoating is the best form of coating available.

Digital camera binoculars are binoculars that also contain a digital camera, sometimes situated in between the two objective lenses.

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